The present invention relates to geochemical oil prospecting. It further relates to methods of predicting the nature of an oil-bearing reservoir.
As primary reserves of oil become scarcer and the expense of finding and recovering oil from remote locations or post-primary sources increases, it becomes more important to be able to determine the conditions present within oil-bearing formations as an aid in predicting the likelihood that oil is located in those formations.
Diagenesis includes all processes that convert sediments to rocks between the time of deposition and the onset of thermal metamorphism. Diagnetic processes can be modeled by laboratory-scale experiments, but these involve many assumptions about subsurface conditions that may not be accurate.
One of the reservoir conditions which is significant in predicting oil is the porosity of the reservoir rock. Porous rock is a condition of the presence of oil. The porosity of reservoir rock may change due to the effects of reservoir fluids on the rock surfaces. As a formation becomes more porous, by the action of formation water and dissolved ionic species (etching), the likelihood of oil migration into that formation increases. As the formation becomes less porous by occlusion, or precipitation, the possibility of recovering oil decreases. Thus, a study of the processes of etching and occlusion in a given formation can provide information on the porosity of the reservoir which can be used in making predictive models of the petroleum potential of the formation.
It is thus an object of the invention to determine the nature of the diagenetic processes occurring in subsurface formations. It is a further object to make models of subsurface formations in order to predict the likelihood of finding oil in the formation.